A 92-year-old woman of Portuguese origin with hypertension, diabetes, and end-stage renal disease presented with atraumatic left-sided back pain. She denied fever, chills, cough, dyspnea, or lower-extremity edema. Evaluation revealed a large left-sided pleural effusion (Fig 1
). Pleural fluid was grossly bloody, with pH 7.12; RBCs, 99,200/μL; WBC count, 7,200/μL (mononuclear cells, 63%; polymorphonucleocytes, 26%; lymphocytes, 8%; and eosinophils, 3%); protein, 4.3 g/dL; lactate dehydrogenase, 11,614 IU/L (serum lactate dehydrogenase, 243 IU/L); and glucose < 10 mg/dL. After an indwelling thoracostomy tube was placed, the patient was discharged without a definitive diagnosis. Two weeks later, she returned noting progressive dyspnea.